The invention relates to a sheet handling device for handling sheets of material, for example sheets of glass and to a method of moving a vertically supported batch of sheets.
Sheets of material are normally formed into a stack so that they can be conveniently handled. In one form of stack they are arranged in face-to-face relationship with the faces of adjacent sheets substantially vertical and in contact with one another. The number of sheets in any one stack is set so that the size of the stack does not exceed the handling capabilities of a stack handling device. In order to conserve space in the warehouse it is convenient to stand the stacks in line with spacers between adjacent stacks. The spacing between adjacent stacks enables the stack handling device to lift stacks individually and convey them away without disturbing other stacks in the line.
In operation a stack handling device having lower and upper pairs of support feet and arms mounted on vertical stanchions is moved towards a stack of sheets vertically mounted on a rack or pallet until the bottom support feet extend under and beyond the stack. The upper arms are then lowered towards the top of the stack, and have at their ends depending projections which locate behind the top edge of the back sheet in the stack to act as a support for the sheets in a horizontal direction. The bottom support feet can then be raised to lift the stack away from its rack or pallet and convey the stack elsewhere. During the lifting and conveying operation the stack of sheets is supported vertically from beneath by the bottom support feet and in a horizontal direction by the projections depending from the upper arms.
This stack handling device has certain limitations. For example, although it can be used for lifting individual stacks away from an array of stacks standing in line at spaced intervals it cannot safely be used to move a stack whose back sheet, i.e. the sheet remote from the main body of the stack handling device, is in face-to-face contact with a substantially vertical support surface which will not allow the bottom support feet to extend beyond the back sheet. For example the substantially vertical support surface may be a wall against which the back sheet is leaning. Furthermore, it is not practical to use the known sheet handling device for lifting a batch of sheets which form a part of a stack of sheets.
The substantially vertical support surface for the back sheet of the batch is another sheet in the remainder of the stack which is in face-to-face contact with the back sheet in the batch. To attempt to lift a batch of sheets could result in considerable damage to the sheets and could also be a considerable safety hazard.
This is a problem when handling stacks of glass sheets and a glass sheet has broken somewhere within a stack. The broken sheet must be removed before the stack can be transported. The broken glass sheet can be reached by using a suction device employing a plurality of suction heads which by suction lift the glass sheets off and away from the stack one at a time, until the broken sheet is reached. Such an operation is very time consuming and laborious.
Furthermore, because the known sheet handling device has limited sheet handling capabilities the stacks of sheets have to be restricted in depth and adjacent stacks have to be spaced apart to an extent such that one stack can be lifted and conveyed away without interfering with other stacks. This is a constraint on the quantity of sheets which can be transported at any one time, for example in a truck or railwagon. There is, therefore, a need to be able to transport larger stacks of sheets and to provide a handling device which can split larger stacks into a variety of smaller stacks of a size or sizes dictated by customers.